Oh, but I actually do have a reason I HAVE to use S-cards.... Read on.... (LOL!!!)

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Normally, I would agree, but at the time, my local Comcast office had absolutely no M-cards in stock to hand out to me. I realize this is a RARE occasion & probably the ONLY reason to have S-cards for a TiVo these days. Trust me, I TRIED to even get M-cards for my two Series 3 (OLED) units, but they didn't have them to hand out. Therefore, I just decided to get 4 S-cards they did have in stock since the rep was only charging me $1.50 for each. I can handle that for now.

I have even been back to my local Comcast office 3 times to try and trade some of the S-cards I have for M-cards and for some unknown reason, all they had each time were STILL S-cards. Someone here suggested I call Comcast to have them mail M-cards to me & I am sure this is an easy solution to get them, but quite frankly I am afraid to talk to someone directly at Comcast in fear of them looking over my bill more closely and then possibly correcting something with it after seeing charges of only a $1.50 for the cable cards (& $2.50 equipment credits). Then putting back about 4 "outlet fee" charges instead. Therefore, resulting in my bill going through the roof.
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No, for now I'll just stick with the S-cards being billed at a $1.50/month for each of them. I can handle this. Again, I realize this is an unusual situation & probably the only reason to have S-cards. Not the norm for most out there, but then again, Comcast has an unusual billing dept. and practices anyway so nothing surprises me.

As long as they are working, there is absolutely no reason for you to swap out your S3(OLED) s-cards for m-cards. You need 2 for each whatever they are and I seem to recall some people reporting problems using m-cards in single stream mode, but that may not be the case. I've never had anything but m-cards and never more than one installed in any particular TiVo, which really isn't saying much in my case since I only have one TiVo (a THD) with 2 slots. I would be thrilled with the $.50/mo net per TiVo you are paying vs. the $7.45/mo net per TiVo I am paying.

I've seen some outrageous Additional Outlet fees posted here over the years. I'm glad for me Cox does not charge anything for additional outlets so it's just $1.99 per CableCard for me. I guess if/when TiVo releases a 6 tuner unit + Mini with dynamic tuner allocation it should provide long term savings for those paying outrageous AOL and/or CableCard fees right now because of multiple units.

Cox Cable Middle Georgia;

$1.99 per card, $5 for first Additional Outlet Fee, $4 for 2nd AOF and beyond.

I changed to an Digital Economy package, which is cheap, and the fees seemed to have vanished. Only $6 a month for three CC's now.

In NoVa now with 1 m-card and it's free. I think one is free but I used to have 4 (with 2 series 2's). At some point I complained that that they were all in the same house/room and since they did not offer an m-card at that point why was I paying for the other 3, so they just made them all free.

My circumstances is a bit unusual as I own my two cards. I got my first card back in 2004 which went into my RCA DLP. My cable company had only one card that they had for show and since I was the first person to try one they gave it to me for free. This was a Motorola S Card. I moved this card into a 8G Kuro in 2008 and then bought the second card for $125 in 2008 for my other 8G Kuro. This one was a Motorola M Card.
Last year one family member bought out the family member that owned my division and I ended up with two new Motorola M Cards as the transition from the old headend to the new one did not go well. This Thursday one M Card will go into my first TiVo as Rovi ended the data for TV Guide On Screen that is embedded in my two Kuros. I think I will wait to see if TiVo releases the 6 tuner DVR this fall and will put the other M Card in that TiVo.

It's obvious from this thread that just spelling out CableCard + Outlet fees doesn't really mean a whole lot. You have to see those fees in the context of the whole cable bill. For example I pay no Additional Outlet fees (using 3 outlets) and CableCards are only $2.00/month, so I'm guessing my base package cost must be quite siginficantly higher than those that do have to pay those fees.

It's obvious from this thread that just spelling out CableCard + Outlet fees doesn't really mean a whole lot. You have to see those fees in the context of the whole cable bill. For example I pay no Additional Outlet fees (using 3 outlets) and CableCards are only $2.00/month, so I'm guessing my base package cost must be quite siginficantly higher than those that do have to pay those fees.

Good point, in CT using Comcast I pay a listed amount of $1.00/card/month and no outlet fee, but in my case my triple play has a high fixed cost and a good listed discount for this two year package, if I returned one cable card I would save that $1.00 + tax per month, but others in my area pay a little less for the package and a lot more for their cable cards. Comcast pricing matrix is incomprehensible to most people.